There is known an electronic commerce system that enables a user to purchase a product or service through a communication network. In some of such electronic commerce systems, a product or service can be jointly purchased (for example, Patent Literature 1). In a joint purchase (a group buying), a unit price of a product purchased within a target period is determined depending on a number of purchases of the product within the period. As the number of purchases of the product becomes larger (purchasers of the product increases), the unit price of the product becomes lower.
Further, in the electronic commerce system, a link to a communication service such as a Twitter (trademark) service is sometimes provided to a product screen in order to allow the user to submit a comment relating to the product to the communication service. Some of such electronic commerce systems are configured to display a submission screen for submitting the comment when the user clicks on the link and initially display predefined sentences on the submission screen.